1. Field of the Invention
This invention relates generally to consistency measurement for the pulp and paper industry, and is more particularly concerned with a sampling apparatus for accurate, repeatable sampling for the determination of consistency.
2. Discussion of the Prior Art
In the pulp and paper industry it is very important to know the consistency of the process. It is conventional to utilize a consistency transmitter which constantly monitors the consistency and constantly gives a reading. The more highly regarded consistency measurement however is determined by taking a sample by hand, and analyzing the sample. A plurality of samples is generally taken, and an average is used as the actual consistency. Consistency transmitters, the, are calibrated on the basis of the hand sample.
In taking a hand sample, one uses a valve in the process line that can be opened so a beaker can be filled. In a effort to obtain a homogeneous and representative sample, one usually allows the liquid to run from the valve for a period of time before filling the beaker. Also, the nipple to which the valve is fixed extends into the process line, beyond the wall of the line, in an effort to avoid the unrepresentative material at the wall of the process line. Even with these various precautions, it will be understood that a major problem is in simply filling the beaker. No two people will read the markings on the beaker precisely the same, and one person will not be very consistent between a plurality of different samples. Overall, it is thought that the hand sampling for the determination of consistency has errors of about ten percent. It is important to remember that the hand sampling is the standard, and the consistency transmitters are calibrated based on the findings through hand sampling. Thus, there is no highly accurate means for determination of consistencies.
The present invention provides a sampling method and apparatus that extracts a quantity of material from the process line, and fills a container having a predetermined volume. A larger quantity than required is drawn to be sure a representative sample is taken, and the container is filled from this quantity. The container is then isolated from the process line, and the sample is deposited into a collector. Clean water is used to wash the sample from the container so the container will be ready to receive another sample.
In the preferred embodiment of the present invention the apparatus includes a chamber in communication with the process line, and a piston reciprocable within the chamber. Rearward movement of the piston causes intake of a quantity of the process; and, the piston uncovers the sample container so process runs into the container. The reverse stroke of the piston urges excess process out of the chamber back into the process line, and closes the container so the container has a discrete volume of process therein. When the process is drained from the sample container it is directed to a filter where the fibers are filtered from the liquid component. Thus, the sample taken is accurate, and repeatable to a high degree of accuracy.